The present invention concerns heating elements for operation at temperatures in the order of 1000.degree. and higher up to 1900.degree. C. Previously known elements of this nature include enveloped infrared lamps, and air exposed filamentary heating elements of refractory compounds and alloys. Available elements include those of chrome-iron alloy, silicon carbide and molybdenum disilicide. Infrared lamps with quartz bulbs have advantages up to 1000.degree. C. bulb temperature but are subject to devitrification if handled improperly. The chrome-iron alloy filaments are limited to 1200.degree. C., require bulky ceramic supports and periodic pre-oxidation for corrosion resistance. They have low power loading (e.g. 30 to 40 watts per inch squared, low electrical efficiency and are subject to attack by materials being treated in the oven or furnace such as salts, glazes, enamels, hydrocarbon and nitrogen. The silicon carbide and molybdenum disilicide filaments attain temperatures of 1500.degree. to 1800.degree. C. but are very fragile and expensive, have low electrical efficiency at high cost. Silicon carbide can carry only a low power loading of thirty five watts per inch squared.
There remains a need for a heating element which is chemically inert and impervious to oxidation, has a high operating temperature (up to 1900.degree. C.), and a high power loading (e.g. 1000 watts per square inch; 100 watts per linear inch). Further the element should be inexpensive itself and should not require expensive supports or fixtures, and should be of rugged construction and easy to install and replace.